For more than a year, the Democratic National Committee touted its "unprecedented" plan to prohibit corporate and lobbyist funding of the 2012 convention in Charlotte, but it found it just couldn't put on a show without the money.

The convention's host committee has acknowledged that it established a separate entity to help shoulder the costs of many of the convention activities this week. That entity, New American City, Inc., has accepted millions of dollars from companies that include Bank of America, Wells Fargo, and most prominently Duke Energy, the nation's largest electric utility, which has sponsored events all over town.

"What was declared was that the convention would be funded differently, and it has been," said Suzi Emmerling, a spokeswoman for the convention host committee.

The lobbyist and corporate money ban held firm for expenses such as designing the stage in the Time Warner Arena and the shuttling of delegates around Charlotte, Emmerling said. But other expenses -- welcome events, concerts, hospitality suites, and more -- are all being underwritten by corporate and union backers.

Duke Energy's CEO Jim Rogers oversaw the host committee effort, and his company has emerged as one of the biggest financial backers of the three-day event. Neither the company nor the host committee will reveal how much Duke gave, but the number is sizeable.

Emmerling said a decision was made by host committee officials to withhold those details until they become public in October, when the committee files its financial reports with federal officials. She could not provide a reason for why dollar amounts from each corporate donor would, for now, remain secret.

"That was a mutual decision between many parties," she said.

Duke Energy spokesman Thomas Williams told ABC News that Jim Rogers had commitments from local companies for $10 million to $11 million before Charlotte was selected as the host city and Duke Energy offered up a $10 million line of credit. Rogers himself gave $100,000. How much more, the company will not say.

It has also helped to pay for events to entertain the city's Democratic guests -- a concert with singer John Legend, a forum featuring former Secretary of State Madeleine Albright, a party at the NASCAR Hall of Fame.

As for the reasons behind Duke Energy's donations, Williams points to community boosterism -- Rogers' desire to see the Charlotte-based company promote its home city on a national stage.

Experts who have studied the influence of money on the political process have a different theory as to why corporations such as Duke Energy invest so heavily.

"What you are seeing are companies demonstrating their loyalty, their willingness to play the game," said Lawrence Lessig, a Harvard Law professor who authored the book "Republic, Lost. How Money Corrupts Congress."

"It's all about business," he said. "It's about building relationships that businesses need in a world where the government is so deeply enmeshed in giving privileges or in enabling government spending or regulating the ways it affects the life and death of these businesses."

Duke Energy faces an array of high-stakes issues in Washington.

Duke received more than $200 million in federal stimulus funds prior to the Charlotte announcement. While Duke was in the midst of committing its funds, federal regulators were reviewing a major merger it was undertaking with a Florida power company -- a merger that has now been approved. Still to be determined -- whether the Nuclear Regulatory Commission will extend the license for a nuclear plant in Florida.

Dozens of more granular issues are under consideration by Congress at any given time. Duke Energy has spent in excess of $5 million on federal lobbying in each of the past four years, and is on pace to spend even more money this year.

Jack Abramoff, one of the most powerful lobbyists in Washington before he was convicted on bribery-related charges in 2006, told ABC News that major companies see the conventions as an enormous opportunity to wine and dine public officials.

"They're people who want something back," said Abramoff, who has championed reform since being released from prison. "They're doing it because they have an agenda."

Williams confirmed that Duke Energy's lobbyists have been having an extremely busy work week.

"I know they're here and going to lots of parties," he said.

But he disputes the idea that the company's decision to help underwrite the Charlotte convention was in any way motivated by a desire to sway the actions of elected officials.

"It's not about trying to curry special favor," he said. "We win whenever Charlotte wins. We are a civic booster, we are expected to take a role in these civic efforts. We have in the past and we will in the future."